Pennsylvania Governor Tom Wolf vowed that the state "will have a fair election and that election will be free from outside influences.”

"Make no mistake, our democracy is being tested in this election."

This seemed to be a reference to the Trump campaign's challenge to the count of votes after Election Day. Some three million votes were mailed in under changes to electoral laws enacted in 2019, Wolf said.

“We are approaching 50 percent of the mail-in ballots counted,” Secretary of State Kathy Boockvar said, adding it was “exactly” where the officials said the process would be by now.

"We are going to accurately count every single ballot," Boockvar added.

“We’re going to defend this vote, the vote by which Joe Biden has been elected to the presidency,” Biden campaign adviser Bob Bauer says during the 'election protection briefing', calling the Republican claims about alleged irregularities in vote-counting "absurd" and "specious."

Pennsylvania remains a key battleground, with its 20 electoral votes in the balance. State Attorney General Josh Shapiro, a Democrat, told CNN the final count won't be done before Friday.

Regardless of what the media or Biden may say, "Vote counts have to be certified. We do this the legal way, not the DC way," said Richard Grenell, former acting director of national intelligence and now a Republican campaign official.

The Biden campaign is holding an "election protection briefing" any minute now, while the Trump campaign has announced a press conference in Philadelphia, Pennsylvania for 3:30 pm local time (2030 GMT).

AP has called Wisconsin for Biden, who was just over 20,000 votes ahead as of the last count.

Trump's campaign manager said they intended to request a recount, which Wisconsin law allows because the difference was within one percentage point.

The Trump campaign said it has filed a lawsuit with the Michigan Court of Claims to halt ballot counting in the state until it is granted “meaningful access” to observe the opening and counting of ballots. Campaign manager, Bill Stepien, also demanded a review of ballots that were allegedly opened and tallied without the campaign representatives present.

Maine’s Republican Senator Susan Collins has claimed victory in her re-election contest against a Democratic contender. Her opponent Sara Gideon confirmed she had already congratulated Collins on winning the vote.

Trump maintains an eight percent lead over Biden in Pennsylvania, with 80 percent of the estimated ballots counted, according to Edison Research. The incumbent has 53.4 percent of the votes while his Democratic contender has 45.3 percent.

With some 100,000 ballots left to count, Michigan expects to present the voting results by Wednesday night, Secretary of State Jocelyn Benson said as she asked “for patience.” “I’m optimistic that by the end of the day, the majority of our ballots will be tabulated,” she told journalists.